1. Field of the Invention
The present invention relates to a brake system for a vehicle, including at least one wheel brake and a master cylinder for outputting a liquid pressure corresponding to a braking operation quantity, an operation quantity detector for detecting a braking operation quantity, a braking pressure control means for outputting an electric signal corresponding to a target braking pressure determined on the basis of a detection value detected by the operation quantity detector, an electric actuator capable of outputting a liquid pressure corresponding to an output electric signal from the braking pressure control means, and a switch-over valve capable of switching the connection and disconnection between the master cylinder and the wheel brake, the electric actuator being connected to the wheel brake for blocking the flow of working liquid from the wheel brake into the electric actuator when the switch-over valve permits the master cylinder and the wheel brake to be put into communication with each other.
2. Description of the Prior Art
Such a system has been conventionally known, for example, from Japanese Patent Application Laid-open No. 95556/92.
In such prior art brake system, the output liquid pressure from a liquid pressure source, for outputting a given liquid pressure, is adjusted in accordance with a braking operation quantity and is outputted from the electric actuator. During a normal braking operation, an output liquid pressure from the electric actuator is applied to the wheel brake. But when the output liquid pressure from the liquid pressure source is abnormally reduced due to a defect in liquid pressure, or the like, the switch-over valve permits the output liquid pressure from the master cylinder to be applied to the wheel brake. However, even if the output liquid pressure from the liquid pressure source is normal, if there is a trouble in the electric actuators, themselves, or an electric circuit for driving the electric actuators, or a trouble in the operation quantity detector for detecting braking operation quantity, a braking pressure, intended by a vehicle's driver, may not be provided in some cases.